1. FIELD OF THE INVENTION
The present invention relates to a method of tracing a drawing and an apparatus for embodying this method, more particularly, the invention relates to a method of tracing a cubic view and an apparatus for implementing this method.
2. DESCRIPTION OF THE PRIOR ART
FIG. 9 schematically illustrates a block diagram of a conventional CAD system which is capable of tracing each cubic view.
In the same way as is normally found in any conventional CAD system, the main unit 1 of this conventional CAD system incorporates a function to draw straight lines, circles, and ellipses.
(A) Straight line:
I. Using a mouse 12 and cursor, this CAD system designates the initiating and terminating points of each straight line to be drawn.
II. This CAD system designates the initiating point of each straight line to be drawn and inputs data of angle and length via an operation keyboard 11.
(B) Circle:
I. Using the mouse 12 and cursor, this CAD system designates the center point and inputs data of radius via the operation keyboard 11.
II. Using the mouse 12 and cursor, this CAD system designates two points corresponding to diameter.
(C) Ellipse:
I. Using the mouse 12 and cursor, this CAD system designates the center point and inputs data of the direction and length of a long diameter and a length of a short diameter.
Using those functions described above, this conventional CAD system can execute a drawing operation. Furthermore, this conventional CAD system can convert a figure drawn on a paper into vector data after tracing it.
More particularly, a memory means accommodated in the main unit 1 stores a figure drawn on the paper by an image scanner 2, and then activates a display unit 13 to display this figure on a display screen as a draft plan. Then, the CAD system traces the draft plan by activating the above function to draw straight lines, circles, and ellipses.
In consequence, the draft plan is converted into vector data, and in addition, the CAD system can output a fair plan via a plotter or a printer 3.
However, it is essential that a tracing operation be executed in perfect accord with those straight lines, circles, and ellipses of the draft plan.
In the event that the draft plan is actually a plane figure like a design plan comprising straight lines and circles, a tracing operation can easily be implemented. Concretely, a straight line can correctly be traced merely by designating the initiating and terminating points. Likewise, in the event that a draft plan solely comprises circles, since the center position and radius are previously identified in many cases, even when the center position is uncertain, a relatively accurate tracing operation can be executed by designating a pair of points corresponding to a diameter as mentioned above.
On the other hand, when tracing a cubic view, it is essential that an ellipse be traced with utmost accuracy. However, as a whole, an ellipse is drawn merely by applying an elliptic rule, and yet, unlike a plane figure, in many cases, the center point is not explicitly identifiable. In consequence, when introducing a method to determine the center point by initially designating the center point of an ellipse, like the conventional method of drawing an ellipse mentioned above, the center point is merely designated by visual estimate. In consequence, it is quite difficult for any conventional method to correctly draw such ellipses each having identical magnitude (in other words, each having lengths of long and short diameters coinciding with each other) at specific positions correctly matching those positions of the draft plan.